The invention relates to a switch controller or regulating switch for regulating a dc output voltage. The switch controller has a regulating path formed of an inductance and a smoothing capacitor. A dc potential is obtainable at the smoothing capacitor. This dc potential is provided at one input of an amplifier which serves for amplifying a difference between this dc potential and a prescribed reference voltage. A pulse-width modulator controls a switching transistor of the switch controller.
Switch controllers (also known as regulating switches) are notoriously known in power supplies for generating a constant output voltage. A regulating path formed of an inductance and of a capacitor is directly charged in pulse-like fashion with a current by a switching transistor (secondary switch controller), or is charged with a current via a transformer and a rectifier diode (flow converter). The regulating path serves for smoothing the voltage applied in pulse-like fashion. A control loop contains a regulating path, including an amplifier for amplifying the difference between the voltage output by the secondary switch controller and a prescribed reference voltage. It further contains a switching transistor and a pulse-width modulator for controlling the pulse-duty factor of the switching transistor. The output voltage is thus controlled to a constant value. A transformer does not change the phase relation but only the voltage and current ratios.
The regulating path formed of the inductance and of the capacitor represents a delay circuit of the second order for the DC voltage modulated by the non-steady final control element, i.e. by the switching transistor. When an extremely slight ripple of the output voltage is required in the switching frequency range, then this delay must have a very high attenuation. A lower resonant frequency of this arrangement thus results which comes close to the noise frequency of the line ac. Given employment of proportional regulators in the control loop, the resonant frequency of the closed control loop is in the proximity of the resonant frequency of the regulating path, because the phase rotation of the closed loop is less than 180.degree. here. Given the resonant frequency of the closed control loop, the loop gain is equal to 1. Due to stability reasons, the loop gain in the noise frequency range, i.e. in the proximity of the resonant frequency of the regulating path, is extremely limited and the disturbance, i.e. the rectified line ac, is only incompletely leveled.
The use of controllers with differential components in the control loop for increasing the loop gain in the noise frequency range is only possible to a very limited degree given switched power supplies, since among other things, they also amplify disturbances resulting from switching events such that the functional reliability is not guaranteed.
The use of steady regulators is known for regulating the output voltage of switched power supplies. These have a very low efficiency. The use of complex control loop structures is also known for regulation such as, for example, an underlying current regulation. This has the disadvantage that an increased component expense is necessary for the current measurement and the current regulator. It is likewise known to reduce the disturbance for a regulated output voltage by means of increased expense for filtering the line voltage ripple.